Inter-resonator coupling

ABSTRACT

In a multi-pole filter the coupling between adjacent cavity resonators is varied in accordance with the distance between the back wall of each cavity and the interconnecting conductor. A section of the interconnecting conductor is so shaped and mounted to assume different spacings from the wall of the cavity according to its rotary position. Means may be provided for locking the connecting conductor in position to set the desired spacing.

United States Patent 91 Hanft INTER-RESONATOR COUPLING [76] Inventor:Herbert Hanft, 1412 Ivanhoe Street,

Alexandria, Va. 22304 [22] Filed: June 3, 1971 21 Appl. No.: 149,620

[52] U.S. Cl ..333/73 C, 333/82 B [51] Int. Cl..-. ..H0lp 1/20, HOlp7/04 [58] Field of Search ..333/73, 73 C, 24, 31, 82 B [56] ReferencesCited UNITED STATES PATENTS 2,919,418 12/1959 Reis ..333/3l 3,159,80312/1964 Czubiak 3,624,563 '11/1971 Burley ..333/24 1 March 6, 19732,851,666 9/1958 Kfich ..333/73 C Primary ExaminerPaul L. GenslerAttorney-F. l-l. Henson and E. P. Klipfel [5 7] ABSTRACT In a multi-polefilter the coupling between adjacent cavity resonators is varied inaccordance with the distance between the back wall of each cavity andthe interconnecting conductor. A section of the interconnectingconductor is so shaped and mounted to assume different spacings from thewall of the cavity according toits rotary position. Means may beprovided for locking the connecting conductor in position to set thedesired spacing.

7 Claims, 3 Drawing Figures INTER-RESONATOR COUPLING CROSS-REFERENCES TORELATED APPLICATIONS The output coupling is in the output cavityresonator and connects the multi-pole filter to a combining network andhence to an antenna.

In copending patent application Ser. No. 838,999, filed July 3, 1969,now U.S. Pat. No. 3,624,563, by Henry E. Burley and William H. Martin,entitled A Fixed Input Coupling Combination For Narrow Band TunableFilters Suitable For Multi-Coupler Applications, assigned to the presentassignee, there is disclosed and claimed an input coupling wherein theinner conductor of the input cavity resonator is connected to agenerator through a choke which is connected at one end to the generatorand at the opposite end by a tap to the inner conductor of the cavity.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates generally to a multistage filter and more particularlyrelates to an adjustable inter-resonator coupling for RF power from oneresonator to the other in a stepless manner over a specificrange.

2. Description of the Prior Art In prior art multi-stage filters the RFpower is coupled from the first resonant cavity to the second resonantcavity by means of an inter-resonator conductor soldered to therespective center conductors of each resonator. The second resonator iscoupled to the third resonator, which 'may be the output resonator, inthe same way. When the inter-resonator conductor is SUMMARY OF THEINVENTION Briefly, the present invention permits the interresonatorcoupling in a multi-resonator filter to be ad justable in a steplessfashion. It has a conductor member so shaped and mounted to assumedifferent spacings from the wall of the cavity according to its rotaryposition. The present invention permits setting of the filter in fieldoperation and in addition permits simplified manufacture and assemblyprocedures.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, reference may be had to the preferred embodiment, exemplaryof the invention, shown in the accompanying drawings, in which:

FIG. 1 shows an illustrative embodiment of the present invention;

FIG. 2 is a cross-sectional view of the present invention; and

FIG. 3 is an isometric illustration of the present invention in anoutput cavity resonator.

DETAILED DESCRIPTION OF THE INVENTION A three-pole multi-stage filter isillustrated in FIG. 1. The resonant cavities 2, 4 and 6 are mountedadjacent each other with each including a center conductor 10foreshortened by a variable capacitor 12. An interresonator coupling 14connects the center conductor of each adjacent cavity resonator. Thecoupler 14 includes a section 16 which is rotatably mounted so that itsouter surface will assume different separation distances from the wallof the cavity according to its rotary position. When the surface of thesection 16 is closer to the back wall of its cavity, the couplingbetween adjacent cavity resonators will be smaller. Increased couplingis obtained by increasing the distance of the sectionv 16 from the wallof the cavity. Section 16 is illustrated to be circular in crosssectional shape although other cross-sectional shaped such as ellipticalcould also be used. 1

FIG. 2 illustrates the adjustable inter-resonator coupling in greaterdetail. The connecting conductor includes the conductor member 16 whichis rotated in position about its off-center axis/A socket head cap screw18 secures the conductor member 16. in its desired rotary position. Anaccess hole 20 in the center conductor 10 allows access to the screw 18.The connecting conductor 22 extends between adjacent cavities andelectrically connects adjacent center conductors.

The cross-sectional view in FIG. 2 shows that the area of contactbetween members 22 and 16, and also 16 and 10 consists of the areabetween two concentric circles. That is, it is a much smaller area thanthe outer diameter of conductor 22. The pressure per unit area exertedby tightening the screw 18 is much greater for this configurationbecause of the small contact area. This type of joint is made betweenmembers that have been buffed, heavily silver plated, and buffed again.The R.F. joints made in this manner provide a molecular silver-to-silvercontact, which has better R.F. conductivity than hard silver solderedjoints. The same type of joint is used between the center conductor andg the cavity, and also between the center conductor and capacitorgooseneck.

From FIG. 3 it can be seen that as the conductor memberis rotated thedistance between the back wall 24 of the cavity and the outer surface ofthe conductor member will vary in accordance with its rotary position.It may be adjusted over the required range by simply loosening thesocket head cap screw 18 and rotating the conductor member 16, and thensecuring its position by tightening the screw 18. The electrical effectis essentially due to the change in distance between the inter-resonatorconductor and the cavity wall. The response of the filter is in partdetermined by the amount of inter-resonator coupling between resonators.

Thus, it should be readily apparent that an interresonator coupling hasbeen provided which is adjustable over a given range of coupling by asimple mechanical means. The inter-resonator coupling minimizes powerloss because of its size and improves R.F. connection because of novelR.F. joints. A more accurate control of the response of the filter isobtainable due to the more precise adjustment of the inter-resonatorcoupling. A I

While the present invention has been described with a degree ofparticularity for the purposes of illustration, it is to be understoodthat all modifications, suggestions and alternations within the spiritand scope of the present invention are herein meant to be included.

I claim as my invention:

1. In a multi-stage filter including a plurality of cavity resonators,each with a center conductor and a back wall, wherein adjacentresonators have outer walls in contact one with another; a rotatableconductor electrically connecting the center conductors of adjacentcavity resonators through apertures in said outer walls and so shapedand mounted to assume different spacings from the back wall of eachcavity according to its rotary position for adjusting inter-resonatorcoupling between said resonators.

2. The combination of claim 1 including means for locking said rotatableconductor in rotary position when the desired inter-resonator couplingis set.

3. An inter-resonator coupling, comprising in combination; a pluralityof cavity resonators, each enclosed by outer walls and each including acenter conductor; and a rotatably mounted conductor electricallyconnecting the center conductors of adjacent cavity resonators throughsaid outer walls and so shaped and mounted to assume different spacingfrom a selected wall of each cavity according to its rotary positionwhereby the range of coupling required between cavity resonators isspanned.

4. In a multi-stage filter, the combination comprising; a plurality ofcavity resonators, each enclosed by outer walls and each with a centerconductor; a connecting conductor extending from the center conductor ofone cavity to the center conductor of an adjacent cavity throughapertures in said walls; a section of said connecting conductor soshaped and mounted to assume different spacings from a selected wall ofthe cavity according to its rotary position.

5. In a multi-stage filter, the combination comprising: a plurality-ofcavity resonators disposed adjacent each other, each with a back walland each with a center conductor; and a conductor member connectingcenter conductors of adjacent cavities and mounted on an off center axisso that its outer surface will assume different distances from the wallof acavity according to its rotary position.

6. The combination of claim 5 wherein said conductor member is circularin cross-section.

7. The combination of claim 5 wherein the cross-section of saidconductor member is elliptical.

1. In a multi-stage filter including a plurality of cavity resonators, each with a center conductor and a back wall, wherein adjacent resonators have outer walls in contact one wIth another; a rotatable conductor electrically connecting the center conductors of adjacent cavity resonators through apertures in said outer walls and so shaped and mounted to assume different spacings from the back wall of each cavity according to its rotary position for adjusting inter-resonator coupling between said resonators.
 1. In a multi-stage filter including a plurality of cavity resonators, each with a center conductor and a back wall, wherein adjacent resonators have outer walls in contact one wIth another; a rotatable conductor electrically connecting the center conductors of adjacent cavity resonators through apertures in said outer walls and so shaped and mounted to assume different spacings from the back wall of each cavity according to its rotary position for adjusting inter-resonator coupling between said resonators.
 2. The combination of claim 1 including means for locking said rotatable conductor in rotary position when the desired inter-resonator coupling is set.
 3. An inter-resonator coupling, comprising in combination; a plurality of cavity resonators, each enclosed by outer walls and each including a center conductor; and a rotatably mounted conductor electrically connecting the center conductors of adjacent cavity resonators through said outer walls and so shaped and mounted to assume different spacing from a selected wall of each cavity according to its rotary position whereby the range of coupling required between cavity resonators is spanned.
 4. In a multi-stage filter, the combination comprising; a plurality of cavity resonators, each enclosed by outer walls and each with a center conductor; a connecting conductor extending from the center conductor of one cavity to the center conductor of an adjacent cavity through apertures in said walls; a section of said connecting conductor so shaped and mounted to assume different spacings from a selected wall of the cavity according to its rotary position.
 5. In a multi-stage filter, the combination comprising: a plurality of cavity resonators disposed adjacent each other, each with a back wall and each with a center conductor; and a conductor member connecting center conductors of adjacent cavities and mounted on an off center axis so that its outer surface will assume different distances from the wall of a cavity according to its rotary position.
 6. The combination of claim 5 wherein said conductor member is circular in cross-section. 